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Gene linkage and polyploidy

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Presentation on theme: "Gene linkage and polyploidy"— Presentation transcript:

1 Gene linkage and polyploidy
Ch 10.3

2 Gene linkage Chromosomes contain genes for a lot of proteins
Genes that are on the same chromosome are usually inherited together. These genes are considered linked.

3 Polyploidy Occurrence of one or more extra sets of all chromosomes in an organism Triploid= 3n. 3 complete sets of chromosomes Earthworms, goldfish, some flowering plants

4 Complex Patterns of Inheritance
Chapter 11.2

5 Extending Mendelian genetics
Mendel worked with a simple system traits were controlled by a single gene each gene had only 2 alleles, one of which is completely dominant to the other The relationship between genotype & phenotype is rarely that simple

6 Incomplete Dominance Dominant and recessive phenotypes are blended in heterozygotes Example: In snapdragons, the alleles for red flowers (CR) and white flowers (CW) both influence the phenotype CRCR = red CWCW = white CRCW = pink

7 Incomplete dominance P F1 100% F2 1:2:1 X true-breeding white flowers
Incomplete dominance true-breeding white flowers true-breeding red flowers X P 100% pink flowers F1 generation (hybrids) 100% self-pollinate 25% red 50% pink 25% white F2 generation 1:2:1

8 Codominance Occurs when both alleles for a gene are expressed at the same time in heterozygotes Roan horses are a combination of white and red horses Instead of blending they have patches or red or white hair.

9 Codominance – Sickle cell anemia
Blood is sickle shaped Decreased ability to transport oxygen block circulation in small blood vessels

10 Codominance – Sickle cell anemia
Homozygous dominant (SS)– healthy Heterozygous (Ss)– some sickled some healthy blood cells. Malaria resistant. Homozygous recessive (ss)– all sickled cells. Fatal.

11 Multiple Alleles Some traits are determined by more than two possible alleles. Example: human blood type (ABO) Alleles: IA, IB, i Rh +/- gene genotype phenotype Donor status IA IA , IA i type A A IB IB, IB i type B B IA IB type AB universal recipient i i type O universal donor

12 Multiple Alleles – rabbit coat color
Four possible alleles for coat color: C, cch, ch, and c Dominance order : C > cch > ch > c Increases number of possible genotypes and phenotypes

13 Epistasis One gene masks another coat color in laboradors - 2 genes
Gene 1 – pigment (C) or no pigment (c) Gene 2 – more pigment (black=B) or less (brown=b) If gene 1 is recessive (cc) the dog will be yellow lab no matter what gene two is. If gene 1 is dominant (Cc or CC) could be black or chocolate lab depending on gene 2

14 Epistasis in Labrador retrievers
Epistasis in Labrador retrievers

15 Chromosomes in Humans Humans have 23 pairs of chromosomes
22 pairs of autosomes 1 pair of sex chromosomes Contain genes that determine gender XX = female, XY = male

16 Sex determination 50% chance for male 50% chance for female
Which parent determines gender?

17 Examples: color-blindness, hemophilia
Sex linked traits Sex-linked traits are coded for by an allele on a sex chromosome. Examples: color-blindness, hemophilia X linked traits more prevalent in males than females.

18 Polygenic inheritance
Some phenotypes determined by additive effects of 2 or more genes for a single character human traits: Skin color Height Eye color Intelligence

19 Chromosomes and Human Heredity
Chapter 11.3

20 Mutations Sex-cell mutations: occur in gametes Affect offspring only
Somatic-cell mutations: occur in body cells Affect the organism only, not inherited Lethal mutations cause death Some mutations are beneficial give organism an evolutionary advantage

21 Chromosome Mutations Deletion – loss of a piece due to breakage
Inversion – a piece breaks off, flips, and reattaches Translocation – a piece breaks off and reattaches to a non-homologous chromosome

22 Chromosome Mutations Nondisjunction – a chromosome fails to separate from its homologue during meiosis One gamete gets an extra copy, the other gets no copies

23 Nondisjunction – Down’s Syndrome
Trisomy 21

24 Fetal testing Testing can be done on fetus before it is born to examine chromosomes. Testing can highlight genetic disorders Testing can be dangerous to mother and fetus.

25 Karyotype Studies A method to study the whole chromosome
Pairs of homologous chromosomes are lined up in decreasing size to produce a micrograph Used for fetal Testing

26 Karyotype Studies

27 Telomeres Telomeres are the protein and DNA caps on the end of chromosomes. Involved in aging of cells.


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